This invention concerns holders for machine tools.
Many cutting or forming tools must be held by a holder with sufficient mechanical interaction (e.g., static and dynamic stiffness, gripping strength, and the like) to enable the tool to perform its intended function on a workpiece as the holder and tool are moved (typically rotated), sometimes at high speed. In modern equipment, tools must be released from the tool holder and replaced with new tools by automated systems. For maximum productivity and cost effectiveness, this process should occur as quickly as possible.
One existing type of tool holder employs a shrink fit, in which the tool holder is heated so that it expands enough to accommodate the tool, and then actively or passively cooled so that it will contract and thus hold the tool during use. This approach involves relatively expensive actuation (heating) equipment, poses safety concerns due to the high temperatures involved for most industrial quality tools having relatively large amounts of metal, and is slower than desired.
In general terms, the invention is a holder for a cutting or forming tool that has two distinct phases. In the first phase, the tool is held with sufficient mechanical interaction between the holder and the tool for the tool to perform its intended purpose on a workpiece. In the second phase, the holder releases the tool sufficiently for it to be rapidly removed, such as by an automated apparatus. The holder may be repeatedly switched between the two phases by application of an external agent, such as by an actuation system of some type (e.g., a heating or cooling system, or a system for applying an electromagnetic field), without degradation of performance (e.g., loss of elasticity). As compared to conventional shrink fit tool holders, the invention provides reduced cost, safer actuation, and reduced time to exchange tools, all of which improve the cost effectiveness of the system.